A lithium metal negative electrode containing a multifunctional polymer brush protective layer and a preparation method therefor, and a lithium metal battery

Abstract

This invention discloses a lithium metal anode with a multifunctional polymer brush protective layer, its preparation method, and a lithium metal battery, belonging to the field of lithium metal anode technology. The preparation method of the lithium metal anode with the multifunctional polymer brush protective layer includes: using surface-initiated atom transfer radical polymerization (SI-ATRP) technology, brominated bacterial cellulose (BC) nanofibers as a matrix are grafted with N-(2-fluorophenyl)acrylamide monomers to synthesize a polymer brush material. Then, a layer of the polymer brush material is coated onto the surface of the lithium metal anode to obtain the anode. The polymer brush protective layer of this invention uses BC as a framework to form a three-dimensional porous network with excellent mechanical properties. The fluorophenyl and amide groups in the polymer brush synergistically optimize lithium-ion transport, reduce the transport barrier, and construct a LiF / LiN composite high ionic conductivity interface, stabilizing the interface, suppressing lithium dendrites, and significantly improving the cycle performance of the lithium metal anode.

Description

Technical Field

[0001] This invention relates to the field of lithium metal anode technology, and particularly to a lithium metal anode with a multifunctional polymer brush protective layer, its preparation method, and a lithium metal battery. Background Technology

[0002] With the continuous growth of energy demand, the energy density of traditional lithium-ion batteries based on graphite anodes limits the development of long-range electric vehicles. To further improve energy density, lithium metal anodes have attracted widespread attention due to their high theoretical capacity, light weight, and low redox potential. However, the uncontrolled growth of lithium dendrites hinders the practical application of lithium metal anodes. Lithium dendrites originate from the high activity of lithium during repeated lithium plating processes and can be extruded from the anode surface, causing severe capacity loss and even puncturing the separator, leading to battery short circuits and thermal runaway.

[0003] The solid electrolyte interphase (SEI) film on the surface of lithium metal anodes plays a crucial role in regulating lithium dendrite growth and improving the stability and cycle life of lithium metal anodes. However, the spontaneously formed SEI film of lithium metal and electrolyte is uneven and fragile, unable to guide the uniform distribution and deposition of lithium ions, nor can it withstand the mechanical stress and tearing caused by the volume expansion of the anode. Preparing a high-performance artificial SEI layer on the surface of lithium metal anodes is an effective method to suppress dendrite growth. Based on material type, artificial SEI films can be divided into inorganic SEI films, organic SEI films, and organic-inorganic composite films. Inorganic SEIs typically possess high mechanical properties and relatively high lithium-ion conductivity, which can suppress the uncontrolled growth of dendrites. Chinese patent CN120221654A prepared an inorganic passivation film containing lithium compounds such as lithium oxide on the surface of lithium metal anodes through impregnation and plasma treatment, thus suppressing dendrite growth. However, during high-capacity charge / discharge of batteries, the rigid inorganic layer exhibits poor interfacial compatibility with lithium metal, making it difficult to adapt to the large volume of the negative electrode, leading to SEI rupture. Furthermore, the introduction of inorganic materials increases electrode mass and reduces battery energy density. Organic SEI films possess better flexibility and interfacial compatibility. Chinese patent CN119050264A uses materials such as polyethylene oxide to prepare a dense, flexible layer on the surface of the lithium metal negative electrode, improving the cycle performance of lithium metal batteries. However, compared to inorganic ionic conductors, the dense organic layer has lower lithium-ion conductivity and lower mechanical strength, making it unable to effectively and rapidly transport lithium ions and suppress dendrite growth. Therefore, combining the advantages of the two artificial SEI films mentioned above, developing an organic-inorganic composite SEI to construct an artificial protective layer with high mechanical modulus, good interfacial compatibility, and high current density tolerance is a crucial step in achieving high-performance lithium metal batteries. Summary of the Invention

[0004] This invention provides a lithium metal anode with a multifunctional polymer brush protective layer, its preparation method, and a lithium metal battery. It can solve the technical problems in the prior art where artificial protective layers cannot synergistically achieve high mechanical modulus to suppress dendrites, good interface compatibility to stabilize the interface, and high lithium-ion conductivity to optimize rate performance.

[0005] In a first aspect, the present invention provides a method for preparing a lithium metal anode containing a multifunctional polymer brush protective layer, comprising the following steps: S1. Preparation of BC-Br; S2. Preparation of polymer brush: Under an inert atmosphere, BC-Br is mixed and stirred with N-(2-fluorophenyl)acrylamide monomers, catalyst, initiator, ligand, and solvent. Then ascorbic acid is added to obtain a mixture. The mixture is reacted, cooled, washed, and dried to obtain a polymer brush. S3. Modification of lithium metal anode with polymer brush protective layer: Disperse the polymer brush obtained in step S2 in an organic solvent, stir to obtain a coating solution, apply the coating solution to the surface of lithium metal, and dry to obtain a lithium metal battery anode with polymer brush protective layer.

[0006] Further, in step S1, the preparation method of BC-Br is as follows: Under a nitrogen atmosphere, BC (bacterial cellulose) was mixed with DMF and anhydrous triethylamine and stirred. Then, BiBB (2-bromoisobutyryl bromide) was added dropwise under ice bath conditions. The mixture was stirred at room temperature, washed, and dried to obtain BC-Br.

[0007] Furthermore, the ratio of BC, DMF, anhydrous triethylamine, and BiBB is 6g:90mL:40g:30g.

[0008] Furthermore, the mixing and stirring time is 2 to 4 hours; the stirring time at room temperature is 20 to 28 hours.

[0009] Further, in step S2, the N-(2-fluorophenyl)acrylamide monomers include any one or more of N-(2-fluorophenyl)acrylamide, N-(2-fluorophenyl)-N-methylacrylamide, N-(2-fluorophenyl)-3-methylacrylamide, N-(2-fluorophenyl)-2-hydroxyacrylamide, and N-(2-fluorophenyl)-N-ethyl-N-methylacrylamide.

[0010] Further, the preparation method of the N-(2-fluorophenyl)-N-methylacrylamide is as follows: In a three-necked flask, N-methyl-o-fluoroaniline, triethylamine, p-hydroxyanisole, and anhydrous dichloromethane were added and stirred to dissolve. The mixture was then cooled to 0°C under nitrogen protection. A mixed solution of acryloyl chloride and anhydrous dichloromethane was added dropwise, with a volume ratio of acryloyl chloride to anhydrous dichloromethane of 1:1. The molar ratio of N-methyl-o-fluoroaniline, acryloyl chloride, and triethylamine was 1:1.1:1.3. The amount of p-hydroxyanisole was 0.1 wt% of the acryloyl chloride. After the addition was complete, the mixture was kept at 0°C and stirred for 4 h. Subsequently, the reaction solution was poured into ice water and stirred for 10 min. The mixture was then separated. The organic phase was washed successively with 1 mol / L dilute hydrochloric acid, saturated NaHCO3, and saturated NaCl, dried over anhydrous Na2SO4, filtered, and recrystallized to obtain N-(2-fluorophenyl)-N-methylacrylamide.

[0011] Further, the preparation method of the N-(2-fluorophenyl)-3-methylacrylamide is as follows: In a three-necked flask, N-methyl-o-fluoroaniline, triethylamine, p-hydroxyanisole, and anhydrous dichloromethane were added and stirred to dissolve. The mixture was then cooled to 0°C under nitrogen protection. A mixed solution of methacryloyl chloride and anhydrous dichloromethane was added dropwise, with a volume ratio of methacryloyl chloride to anhydrous dichloromethane of 1:1. The molar ratio of N-methyl-o-fluoroaniline, methacryloyl chloride, and triethylamine was 1:1.1:1.4. The amount of p-hydroxyanisole was 0.1 wt% of the methacryloyl chloride. After the addition was complete, the mixture was kept at 20°C and stirred for 4 hours. Subsequently, the reaction solution was poured into ice water and stirred for 10 minutes. The mixture was then separated. The organic phase was washed successively with 1 mol / L dilute hydrochloric acid, saturated NaHCO3, and saturated NaCl, dried over anhydrous Na2SO4, filtered, and recrystallized to obtain N-(2-fluorophenyl)-3-methylacrylamide.

[0012] Further, the preparation method of the N-(2-fluorophenyl)-2-hydroxyacrylamide is as follows: N-(2-fluorophenyl)acrylamide was added to formic acid, stirred and dissolved, cooled to 0°C, and 30% hydrogen peroxide was slowly added dropwise. The molar ratio of N-(2-fluorophenyl)acrylamide, hydrogen peroxide and formic acid was 1:1.2:400. The temperature was controlled not to exceed 10°C, and then stirred at room temperature for 6 hours. The reaction solution was slowly poured into ice water and neutralized to weakly alkaline (pH=8) with saturated NaHCO3 while stirring. The organic phase was extracted with ethyl acetate and washed with saturated brine. After drying with anhydrous Na2SO4 and recrystallization, N-(2-fluorophenyl)-2-hydroxyacrylamide was obtained.

[0013] Further, the preparation method of the N-(2-fluorophenyl)-N-ethyl-N-methylacrylamide is as follows: N-ethyl-2-fluoroaniline, triethylamine, p-hydroxyanisole, and anhydrous dichloromethane were added to a three-necked flask and stirred to dissolve. The mixture was then cooled to 0°C under nitrogen protection, and acryloyl chloride was slowly added dropwise. The volume ratio of N-ethyl-2-fluoroaniline to anhydrous dichloromethane was 1:10, and the molar ratio of N-ethyl-2-fluoroaniline, acryloyl chloride, and triethylamine was 1:1.1:1.5. The amount of p-hydroxyanisole was 0.1 wt% of the acryloyl chloride. After the addition was complete, the mixture was kept at 20°C and stirred for 4 hours. Subsequently, the reaction solution was poured into ice water and stirred for 10 minutes. The mixture was then separated. The organic phase was washed successively with 1 mol / L dilute hydrochloric acid, saturated NaHCO3, and saturated NaCl. After drying with anhydrous Na2SO4 and filtration, N-(2-fluorophenyl)-N-ethyl-N-methylacrylamide was obtained.

[0014] Furthermore, in step S2, the catalyst includes any one or more of CuBr2 and CuBr.

[0015] Further, in step S2, the initiator includes any one or more of bromomethylbenzoate (BMBz), ethyl bromophenylacetate (BrPBA), and ethyl bromoisobutyrate (EBiB).

[0016] Further, in step S2, the ligand includes any one or more of 2,2'-bipyridine (bpy) and pentamethyldiethyltriamine.

[0017] Further, in step S2, the solvent includes any one or more of N,N-dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, and methanol.

[0018] Furthermore, in step S2, the inert atmosphere is nitrogen.

[0019] Further, in step S2, based on the total mass of the mixture, the mass percentages of each component are as follows: N-(2-fluorophenyl)acrylamide monomers 25%–35%, BC-Br 2.5%–3%, catalyst 0.05%–0.06%, initiator 0.01%–0.03%, ligand 1.2%–1.6%, organic solvent 60%–70%, and ascorbic acid 0.3%–0.4%.

[0020] Furthermore, in step S2, the mixing and stirring time is 1 to 3 hours.

[0021] Further, in step S2, the reaction time is 24-48 hours and the temperature is 60-90°C; the drying temperature is 60-80°C and the time is 5-10 hours.

[0022] Further, in step S3, the organic solvent includes any one or more of tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide, ethylene glycol dimethyl ether, and 1,3-dioxolane.

[0023] Further, in step S3, the polymer brush has a mass percentage of 0.5% to 5% in the coating liquid.

[0024] Furthermore, in step S3, the stirring time is 3 to 6 hours.

[0025] Furthermore, in step S3, the drying temperature is 60–80°C, and the drying time is 6–10 hours.

[0026] Secondly, the present invention provides a lithium metal anode containing a multifunctional polymer brush protective layer, which is prepared by any one of the preparation methods described above.

[0027] Thirdly, the present invention provides a lithium metal battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode is the lithium metal negative electrode with a multifunctional polymer brush protective layer as described above.

[0028] The beneficial effects of this invention are: 1. The method for preparing a lithium metal anode with a multifunctional polymer brush protective layer provided by the present invention includes the following steps: Step S1: BC-Br is prepared, which can introduce active initiation sites on bacterial cellulose, providing a reliable basis for subsequent grafting reactions; Step S2: Using BC-Br as the initiating matrix and N-(2-fluorophenyl)acrylamide monomers as functional monomers, efficient grafting polymerization is achieved through ascorbic acid reduction regulation in a reaction system composed of catalyst, initiator, ligand and solvent, to obtain a polymer brush with uniform structure and both fluorine function and ion transport characteristics; Step S3: The polymer brush is dispersed in an organic solvent to form a coating solution, which is then applied and dried on the surface of the lithium metal anode to construct a uniform and stable multifunctional protective layer, effectively inhibiting lithium dendrite growth, reducing side reactions and improving interface stability, thereby significantly improving the electrochemical performance of the lithium metal anode.

[0029] 2. The polymer brush protective layer material provided by this invention uses bacterial cellulose as a matrix to construct a stable framework nanonetwork. This not only possesses excellent mechanical strength but also forms a highly porous three-dimensional interconnected structure, providing channels for rapid lithium-ion transport. The grafted polymer brush structure significantly improves the interfacial compatibility between the protective layer and the lithium anode and electrolyte. The amide groups and polar, electronegative groups such as fluorophenyl groups can synergistically regulate lithium-ion transport behavior: fluorophenyl groups can generate moderate interactions with lithium ions, while amide groups can effectively weaken the excessively strong binding energy between lithium ions and fluorine-containing groups, reducing... The low lithium-ion transport barrier optimizes lithium-ion conduction efficiency at the interface. Meanwhile, the fluorine element in the protective layer can induce the formation of a stable interface phase rich in lithium fluoride (LiF), and the nitrogen element in the amide group can further induce the formation of lithium nitride (LiN). The two work together to construct a LiF / LiN composite rigid interface layer with both high stability and high ionic conductivity. This ensures the stability of the interface structure, reduces interface impedance and battery polarization, and fundamentally suppresses the uneven growth of lithium dendrites, achieving long-term protection for the lithium metal anode and significantly improving the cycle stability and overall electrochemical performance of lithium metal batteries. Attached Figure Description

[0030] Figure 1 This is a SEM image of the lithium metal anode with a multifunctional polymer brush protective layer prepared in Example 1 of the present invention; Figure 2 This is a SEM image of the lithium metal anode with a multifunctional polymer brush protective layer after lithium deposition in Example 1 of the present invention. Figure 3 XPS spectra of BC-Br prepared in Example 1 of this invention are provided; where a represents the spectra before and after modification of the hydroxyl characteristic absorption region; b represents the spectra before and after modification of the C-Br bond characteristic absorption region. Figure 4 The NMR spectrum of N-(2-fluorophenyl)-N-methylacrylamide; Figure 5 The NMR spectrum of N-(2-fluorophenyl)-3-methylacrylamide; Figure 6 The NMR spectrum of N-(2-fluorophenyl)-2-hydroxyacrylamide; Figure 7 The nuclear magnetic resonance spectrum of N-(2-fluorophenyl)-N-ethyl-N-methylacrylamide; Figure 8 XPS spectra were obtained to demonstrate the successful preparation of the polymer brush in Example 1 of this invention. Detailed Implementation

[0031] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0032] In a first aspect, the present invention provides a method for preparing a lithium metal anode containing a multifunctional polymer brush protective layer, comprising the following steps: S1. Preparation of BC-Br; While BC alone can physically buffer volume changes, it suffers from drawbacks such as poor insulation, poor ion transport, weak interfacial compatibility, and lack of chemical regulation, making it difficult to suppress dendrite formation. This invention prepares BC-Br and introduces active bromine atoms (Br) onto bacterial cellulose via a bromination reaction. This provides a high density of initiation sites for subsequent surface-initiated atom transfer radical polymerization grafting of N-(2-fluorophenyl)acrylamide functional monomers, ensuring uniform and robust polymer growth on the scaffold surface. This results in an integrated protective layer with both excellent mechanical properties and efficient ion transport.

[0033] S2. Preparation of polymer brush: Under an inert atmosphere, BC-Br is mixed and stirred with N-(2-fluorophenyl)acrylamide monomers, catalyst, initiator, ligand and solvent to obtain a mixture. Then ascorbic acid is added, the mixture is reacted, cooled, washed and dried to obtain a polymer brush. In the above steps, BC-Br serves as the matrix, and the bromine atoms introduced on its surface provide uniformly distributed active sites for the polymerization reaction, ensuring that the polymer adheres firmly to the bacterial cellulose backbone. N-(2-fluorophenyl)acrylamide monomers, as functional monomers, exhibit synergistic effects between the fluorophenyl and amide groups in their molecules. The fluorophenyl group can moderately interact with lithium ions to regulate ion transport, while the amide group weakens the excessively strong binding energy between lithium ions and fluorine-containing groups, lowering the transport barrier. Together, they optimize the interfacial lithium ion conduction efficiency. Simultaneously, fluorine can induce the formation of a highly stable lithium fluoride (LiF) interfacial phase. Nitrogen can further induce the formation of lithium nitride (LiN) with high ionic conductivity, laying the foundation for constructing a LiF / LiN composite rigid interface layer; the complex formed by the catalyst and ligand precisely regulates the activity and controllability of the polymerization reaction, ensuring uniform polymer chain length and regular structure; the initiator assists in initiating the polymerization process, further ensuring the efficient progress of the reaction; the solvent provides a uniform medium environment for the reaction, ensuring that each component is fully dissolved and dispersed; ascorbic acid, as a reducing agent, can effectively regenerate the low-valence active catalyst, maintaining the continuity and stability of the polymerization reaction, and finally obtaining a polymer brush material with uniform structure and excellent performance.

[0034] S3. Modification of lithium metal anode with polymer brush protective layer: Disperse the polymer brush obtained in step S2 in an organic solvent, stir to obtain a coating solution, apply the coating solution to the surface of lithium metal, and dry to obtain a lithium metal battery anode with polymer brush protective layer.

[0035] The above steps disperse the polymer brush in an organic solvent to form a uniform coating solution, which ensures that the protective layer is evenly spread on the lithium metal surface. Through coating and drying, a continuous, dense, and strongly adherent multifunctional protective layer is formed on the negative electrode surface. This layer can physically isolate the electrolyte from the lithium negative electrode and reduce side reactions, while also uniformly dispersing lithium ions and inhibiting lithium dendrite growth. At the same time, it improves interface stability and cycle life, giving the lithium metal negative electrode excellent electrochemical performance.

[0036] In some embodiments, the preparation method of BC-Br in step S1 is as follows: Under a nitrogen atmosphere, BC (bacterial cellulose) was mixed with DMF and anhydrous triethylamine and stirred. Then, BiBB (2-bromoisobutyryl bromide) was added dropwise under ice bath conditions. The mixture was stirred at room temperature, washed, and dried to obtain BC-Br.

[0037] The above steps, performed under nitrogen and ice bath conditions, use anhydrous triethylamine as an acid-binding agent to esterify the hydroxyl groups on BC with BiBB, introducing bromoalkyl groups onto the BC surface to obtain the matrix BC-Br for grafting polymer brushes.

[0038] In some embodiments, the ratio of BC, DMF, anhydrous triethylamine, and BiBB is 6g:90mL:40g:30g. This ratio ensures sufficient dispersion of BC, guarantees efficient reaction between BiBB and hydroxyl groups, and effectively neutralizes byproducts with anhydrous triethylamine, thereby introducing an appropriate amount and uniform active initiation sites on the BC surface, improving bromination efficiency and product stability.

[0039] In some embodiments, the mixing and stirring time is 2–4 hours; the stirring time at room temperature is 20–28 hours. This stirring time range ensures that BC is fully swollen and dispersed, BiBB is uniformly adsorbed and reacts completely with the hydroxyl groups. Too short a time will lead to insufficient bromination grafting and fewer initiation sites, while too long a time will easily cause fiber structure damage, increase side reactions, and affect the subsequent polymerization effect.

[0040] In some embodiments, in step S2, the N-(2-fluorophenyl)acrylamide monomers include any one or more of N-(2-fluorophenyl)acrylamide, N-(2-fluorophenyl)-N-methylacrylamide, N-(2-fluorophenyl)-3-methylacrylamide, N-(2-fluorophenyl)-2-hydroxyacrylamide, and N-(2-fluorophenyl)-N-ethyl-N-methylacrylamide. These monomers contain both fluorophenyl and amide groups, providing both liquid-repellent, interface-stabilizing fluorine elements and nitrogen sites that can induce high ionic conductivity interfaces. These two elements synergistically lower the lithium-ion transport barrier and construct a stable LiF / LiN composite interface. By selecting a variety of structurally tunable monomers, the performance adaptability range of the protective layer can be broadened, ensuring optimal overall interface compatibility, ion transport efficiency, and mechanical stability, thus achieving highly efficient protection of the lithium anode.

[0041] In some embodiments, the method for preparing N-(2-fluorophenyl)-N-methylacrylamide is as follows: In a three-necked flask, N-methyl-o-fluoroaniline, triethylamine, p-hydroxyanisole, and anhydrous dichloromethane were added and stirred to dissolve. The mixture was then cooled to 0°C under nitrogen protection. A mixed solution of acryloyl chloride and anhydrous dichloromethane was added dropwise, with a volume ratio of acryloyl chloride to anhydrous dichloromethane of 1:1. The molar ratio of N-methyl-o-fluoroaniline, acryloyl chloride, and triethylamine was 1:1.1:1.3. The amount of p-hydroxyanisole was 0.1 wt% of the acryloyl chloride. After the addition was complete, the mixture was kept at 0°C and stirred for 4 h. Subsequently, the reaction solution was poured into ice water and stirred for 10 min. The mixture was then separated. The organic phase was washed successively with 1 mol / L dilute hydrochloric acid, saturated NaHCO3, and saturated NaCl, dried over anhydrous Na2SO4, filtered, and recrystallized to obtain N-(2-fluorophenyl)-N-methylacrylamide.

[0042] In the above steps, N-(2-fluorophenyl)-N-methylacrylamide is prepared by a nucleophilic substitution reaction of N-methylo-fluoroaniline and acryloyl chloride. Under nitrogen protection and low temperature conditions, triethylamine acts as an acid absorbent to promote the acylation reaction of acryloyl chloride, p-hydroxyanisole acts as a polymerization inhibitor to prevent the thermal polymerization of acrylate monomers, and anhydrous dichloromethane acts as a reaction solvent to maintain the homogeneity of the reaction system. During the reaction, the aniline amino group attacks the acyl carbon of acryloyl chloride, undergoes a substitution reaction and removes hydrogen chloride, thereby forming a stable amide bond structure under neutral conditions. After post-treatment and recrystallization, N-(2-fluorophenyl)-N-methylacrylamide with high purity is obtained.

[0043] In some embodiments, the method for preparing N-(2-fluorophenyl)-3-methylacrylamide is as follows: In a three-necked flask, N-methyl-o-fluoroaniline, triethylamine, p-hydroxyanisole, and anhydrous dichloromethane were added and stirred to dissolve. The mixture was then cooled to 0°C under nitrogen protection. A mixed solution of methacryloyl chloride and anhydrous dichloromethane was added dropwise, with a volume ratio of methacryloyl chloride to anhydrous dichloromethane of 1:1. The molar ratio of N-methyl-o-fluoroaniline, methacryloyl chloride, and triethylamine was 1:1.1:1.4. The amount of p-hydroxyanisole was 0.1 wt% of the methacryloyl chloride. After the addition was complete, the mixture was kept at 20°C and stirred for 4 hours. Subsequently, the reaction solution was poured into ice water and stirred for 10 minutes. The mixture was then separated. The organic phase was washed successively with 1 mol / L dilute hydrochloric acid, saturated NaHCO3, and saturated NaCl, dried over anhydrous Na2SO4, filtered, and recrystallized to obtain N-(2-fluorophenyl)-3-methylacrylamide.

[0044] In the above steps, under nitrogen protection, anhydrous dichloromethane is used as the solvent. The amino group in N-methyl-o-fluoroaniline acts as a nucleophile, attacking the acyl carbon in methacryloyl chloride to undergo a nucleophilic substitution reaction, removing hydrogen chloride and forming an amide bond. Triethylamine acts as an acid absorber, promptly absorbing the hydrogen chloride generated in the reaction and promoting the forward reaction. p-hydroxyanisole acts as a polymerization inhibitor, preventing the self-polymerization of methacryloyl chloride monomers. Cooling to 0°C controls the reaction rate during the dropping process and avoids side reactions. Stirring at 20°C ensures the reaction proceeds fully. Subsequently, the mixture is quenched with ice water, separated, washed, dried, and recrystallized to remove impurities and obtain high-purity N-(2-fluorophenyl)-3-methylacrylamide.

[0045] In some embodiments, the method for preparing N-(2-fluorophenyl)-2-hydroxyacrylamide is as follows: N-(2-fluorophenyl)acrylamide was added to formic acid, stirred and dissolved, cooled to 0°C, and 30% hydrogen peroxide was slowly added dropwise. The molar ratio of N-(2-fluorophenyl)acrylamide, hydrogen peroxide and formic acid was 1:1.2:400. The temperature was controlled not to exceed 10°C, and then stirred at room temperature for 6 hours. The reaction solution was slowly poured into ice water and neutralized to weakly alkaline (pH=8) with saturated NaHCO3 while stirring. The organic phase was extracted with ethyl acetate and washed with saturated brine. After drying with anhydrous Na2SO4 and recrystallization, N-(2-fluorophenyl)-2-hydroxyacrylamide was obtained.

[0046] In the above steps, using formic acid as a solvent and acidic catalytic medium, the carbon-carbon double bond in the N-(2-fluorophenyl)acrylamide molecule undergoes an epoxidation reaction under the oxidation of 30% hydrogen peroxide. Subsequently, the epoxide bond hydrolyzes to generate hydroxyl groups, thereby introducing hydroxyl groups into the acrylamide side chain. Cooling to 0℃ and controlling the temperature not to exceed 10℃ can inhibit the decomposition of hydrogen peroxide and the occurrence of side reactions. Stirring at room temperature for 6 hours ensures that the oxidation and hydrolysis reactions are fully carried out. Subsequently, the reaction is quenched by ice water, neutralized to weak alkalinity with saturated NaHCO3 to terminate the reaction, and the pH of the system is adjusted. After extraction with ethyl acetate, washing with saturated brine, drying with anhydrous Na2SO4, and recrystallization, impurities are removed and high-purity N-(2-fluorophenyl)-2-hydroxyacrylamide is obtained.

[0047] In some embodiments, the method for preparing N-(2-fluorophenyl)-N-ethyl-N-methylacrylamide is as follows: N-ethyl-2-fluoroaniline, triethylamine, p-hydroxyanisole, and anhydrous dichloromethane were added to a three-necked flask and stirred to dissolve. The mixture was then cooled to 0°C under nitrogen protection. Acryloyl chloride was slowly added dropwise. The volume ratio of N-ethyl-2-fluoroaniline to anhydrous dichloromethane was 1:10, and the molar ratio of N-ethyl-2-fluoroaniline, acryloyl chloride, and triethylamine was 1:1.1:1.5. The amount of p-hydroxyanisole was 0.1 wt% of the acryloyl chloride. After the addition was complete, the mixture was kept at 20°C and stirred for 4 hours. Subsequently, the reaction solution was poured into ice water and stirred for 10 minutes. The mixture was then separated. The organic phase was washed successively with 1 mol / L dilute hydrochloric acid, saturated NaHCO3, and saturated NaCl. After drying with anhydrous Na2SO4 and filtration, N-(2-fluorophenyl)-N-ethyl-N-methylacrylamide was obtained.

[0048] In the above steps, the reaction uses anhydrous dichloromethane as a solvent. Under nitrogen protection, the amino group of N-ethyl-2-fluoroaniline acts as a nucleophile and undergoes a nucleophilic substitution reaction with acryloyl chloride to form an amide bond. Triethylamine acts as an acid-binding agent to neutralize the HCl produced in the reaction and promote the forward reaction. p-hydroxyanisole acts as a polymerization inhibitor to prevent the self-polymerization of monomer double bonds. Dropwise addition at 0°C can control the intensity of the reaction and avoid side reactions. Holding at 20°C ensures the reaction is complete. Subsequently, the reaction is quenched with ice water, washed with dilute hydrochloric acid and saturated sodium bicarbonate to remove impurities, dehydrated with saturated brine, dried with anhydrous sodium sulfate, and filtered to obtain pure N-(2-fluorophenyl)-N-ethyl-N-methylacrylamide.

[0049] In some embodiments, in step S2, the catalyst includes any one or more of CuBr2 and CuBr. As transition metal catalysts, CuBr2 and CuBr can participate in redox cycles, providing stable catalytic active centers for atom transfer radical polymerization, effectively controlling the polymerization reaction rate and grafting uniformity, ensuring a regular polymer brush structure and narrow molecular weight distribution, thereby improving the ion transport and interfacial stability of the protective layer.

[0050] In some embodiments, in step S2, the initiator includes any one or more of bromomethylbenzoate (BMBz), ethyl bromophenylacetate (BrPBA), and ethyl bromoisobutyrate (EBiB). These initiators have high initiation efficiency and moderate activity, and can synergistically construct an efficient and controllable polymerization system with BC-Br, ensuring stable grafting of N-(2-fluorophenyl)acrylamide monomers, resulting in a more uniform polymer brush structure and more stable performance, providing a reliable structural basis for the protective layer.

[0051] In some embodiments, in step S2, the ligand includes any one or more of 2,2'-bipyridine (bpy) and pentamethyldiethyltriamine. The ligand can form a soluble complex with the copper catalyst, improving the stability and reaction uniformity of the catalytic system, effectively controlling catalytic activity, making the graft polymerization mild and controllable, and ensuring that the polymer grows uniformly and structurally regular on the BC backbone.

[0052] In some embodiments, in step S2, the solvent includes any one or more of N,N-dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, and methanol. These solvents exhibit good solubility and dispersibility for BC-Br, monomers, and the catalytic system, ensuring a homogeneous and stable reaction system, promoting full contact and reaction of the components, and facilitating subsequent washing and purification, thereby improving product quality.

[0053] In some embodiments, the inert atmosphere in step S2 is nitrogen. Using nitrogen as the inert atmosphere can effectively isolate interfering components such as oxygen and moisture in the air, avoiding their inhibitory or destructive effects on the catalytic active center, reaction intermediates, and polymerization process, ensuring that the atom transfer radical polymerization reaction proceeds stably, controllably, and efficiently, thereby obtaining a polymer brush with uniform structure and stable performance.

[0054] In some embodiments, in step S2, based on the total mass of the mixture, the mass percentages of each component are as follows: N-(2-fluorophenyl)acrylamide monomers 25%–35%, BC-Br 2.5%–3%, catalyst 0.05%–0.06%, initiator 0.01%–0.03%, ligand 1.2%–1.6%, organic solvent 60%–70%, and ascorbic acid 0.3%–0.4%. This dosage ensures that BC-Br provides sufficient initiation sites and that the monomers form functional brushes of appropriate length and uniform distribution on the backbone surface, providing sufficient fluorine and nitrogen groups to optimize lithium-ion transport and induce the formation of a stable LiF / LiN interface layer. Simultaneously, the synergistic dosage of catalyst, initiator, ligand, and ascorbic acid allows for precise control of the polymerization reaction's controllability and efficiency, while the appropriate solvent dosage ensures the homogeneity and stability of the system. If the amount of any component exceeds this range, it will lead to problems such as excessively dense or sparse polymer brushes, uncontrolled reaction, and uneven structure, which will affect interfacial ion conduction and mechanical stability. However, if the amount is strictly controlled within the preferred range, a protective layer with high ionic conductivity, excellent mechanical properties and stable interface can be synergistically constructed, which will ultimately significantly reduce the battery internal resistance and improve cycle stability.

[0055] In some embodiments, the mixing and stirring time in step S2 is 1 to 3 hours. This time period allows the components such as BC-Br, monomer, catalyst, and ligand to be fully mixed and dispersed evenly, laying a stable system foundation for subsequent reactions; too short a time will lead to uneven dispersion and excessively rapid local reactions, while too long a time will increase the process time without any additional benefit.

[0056] In some embodiments, in step S2, the reaction time is 24–48 hours and the temperature is 60–90°C; the drying temperature is 60–80°C and the time is 5–10 hours. This time and temperature range ensures that the graft polymerization reaction is complete and controllable, with a moderate grafting density and a regular polymer brush structure. Too low a temperature or too short a time will lead to incomplete grafting, while too high a temperature or too long a time can easily trigger side reactions and damage the fiber structure. These drying conditions allow for rapid solvent removal without damaging the polymer structure, ensuring thorough drying of the product. Too low a temperature or too short a time will lead to incomplete drying, while too high a temperature or too long a time can easily cause thermal damage to the material, affecting the performance of the protective layer.

[0057] In some embodiments, in step S3, the organic solvent includes any one or more of tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide, ethylene glycol dimethyl ether, and 1,3-dioxolane. These organic solvents have good solubility in polymer brushes, moderate volatility, and are gentle on lithium anodes, forming a uniform and stable coating solution that ensures a smooth and dense protective film without damaging the lithium metal surface.

[0058] In some embodiments, in step S3, the polymer brush has a mass percentage content of 0.5% to 5% in the coating solution. This dosage range allows the coating solution to have a moderate viscosity and uniform film formation. Too low a dosage will result in a thin protective layer that cannot effectively suppress lithium dendrites, while too high a dosage will easily result in an overly thick and uneven coating, increasing interfacial impedance and affecting lithium ion transport.

[0059] In some embodiments, the stirring time in step S3 is 3 to 6 hours. This allows the polymer brush to be fully and evenly dispersed. If the time is too short, the dispersion will be uneven, and if the time is too long, it will easily introduce air bubbles or damage the structure.

[0060] In some embodiments, in step S3, the drying temperature is 60–80°C and the drying time is 6–10 hours. This allows the coating to dry quickly without damaging the lithium anode. If the temperature is too low or the time is too short, the drying will be insufficient; if the temperature is too high or the time is too long, it may cause damage to the anode and cracking of the coating.

[0061] Secondly, the present invention provides a lithium metal anode containing a multifunctional polymer brush protective layer, which is prepared by any one of the preparation methods described above.

[0062] Thirdly, the present invention provides a lithium metal battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode is the lithium metal negative electrode with a multifunctional polymer brush protective layer as described above.

[0063] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0064] Example Example 1 This embodiment provides a method for preparing a lithium metal anode with a multifunctional polymer brush protective layer, including the following steps: S1. Preparation of BC-Br: Under a nitrogen atmosphere, 6g of BC was mixed with 90g of DMF and 40g of anhydrous triethylamine and stirred for 3h. Then, 30g of BiBB was slowly added dropwise under ice bath conditions, and the mixture was stirred at room temperature for 24h. The product was washed with an ethanol-water solution and then vacuum dried at 50℃ for 12h to obtain BC-Br. Figure 3 It can be seen that, Figure 3 The results showed that the BC sample before bromination modification exhibited a distinct hydroxyl characteristic absorption peak; after bromination, the intensity of the hydroxyl peak decreased significantly, indicating that a large number of hydroxyl groups on the material surface were consumed in the bromination substitution reaction. Figure 3 As can be seen from the infrared signature changes, the unbrominated sample showed no significant characteristic absorption and a stable curve within the C-Br bond characteristic absorption range, while the brominated sample exhibited a significant broad absorption trough, proving the successful introduction of a carbon-bromine bond into the molecular structure. These two infrared signature changes corroborate each other, confirming the successful preparation of BC-Br.

[0065] S2. Preparation of polymer brush: Under a nitrogen atmosphere, 5g of N-(2-fluorophenyl)acrylamide (NFPA), 0.6g of BC-Br, 0.012g of CuBr2, 0.004g of BMBz, 0.314g of pentamethyldiethyltriamine and 14mL of N,N-dimethylformamide were mixed and stirred at room temperature for 3h. Then, 0.07g of ascorbic acid was added, and the mixture was reacted at 80℃ for 24h. The reaction was terminated by cooling to room temperature and exposing the mixture to air. Finally, the mixture was washed several times by centrifugation with distilled water and dried under vacuum at 70℃ for 8h to obtain the BC-g-NFPA polymer brush. Figure 8 These are XPS spectra of the polymer before and after brush grafting, from... Figure 8It can be seen that the binding energy range of 684-689 eV falls within the characteristic peak range of fluorine. Before grafting the fluorinated phenyl polymer brush, the spectral lines of the BC sample were flat with no obvious characteristic diffraction peaks, indicating that there was no fluorine on the surface of the original BC substrate. After grafting modification, the sample showed a significant F1s characteristic absorption peak near 687 eV. This binding energy position corresponds to the characteristic signal of organofluorine chemical bonds, proving that fluorine was successfully introduced into the material surface, which confirms that the fluorinated phenyl polymer brush has been covalently grafted onto the BC matrix surface.

[0066] S3. Polymer brush protective layer modification of lithium metal anode: 0.3g BC-g-NFPA was added to 9.7g tetrahydrofuran and stirred for 4h to obtain a coating solution. The prepared coating solution was coated on the surface of lithium foil and dried at 80℃ for 6h to obtain a lithium metal battery anode with a polymer brush protective layer. Scanning electron microscopy (SEM) images were then performed on the anode. Figure 1 As shown, the polymer brush protective layer is uniformly distributed.

[0067] CR2016 button cells were assembled in an argon-filled glove box. Copper foil with a protective layer was used as the cathode, Celgard 2400 as the separator, and a conventional carbonate electrolyte (1M LiPF6, EC / DMC / FEC (v / v / v = 3 / 7 / 0.5)). Lithium foil was used as the anode, and an ampere was applied at 6 mA / cm². 2 Conditional deposition was performed for 1 hour, and then the battery was removed from the argon-filled glove box and subjected to scanning electron microscopy. The results are as follows. Figure 2 As shown, from Figure 2 It can be seen that lithium deposition exhibits a flat, smooth, sheet-like structure and a dense morphology, without dendrite growth.

[0068] Example 2 This embodiment provides a method for preparing a lithium metal anode with a multifunctional polymer brush protective layer, including the following steps: S1. Preparation of BC-Br: Under a nitrogen atmosphere, 6g of BC was mixed with 90g of DMF and 40g of anhydrous triethylamine and stirred for 3h. Then, 30g of BiBB was slowly added dropwise under ice bath conditions and stirred at room temperature for 24h. After washing the product with an ethanol aqueous solution, it was dried under vacuum at 50℃ for 12h to obtain BC-Br. S2. Preparation of polymer brush: Under a nitrogen atmosphere, 7g of N-(2-fluorophenyl)-N-methylacrylamide (NFMPA), 0.6g of BC-Br, 0.012g of CuBr2, 0.006g of BrPBA, 0.32g of bpy and 12mL of dimethyl sulfoxide were mixed and stirred at room temperature for 2h. Then, 0.062g of ascorbic acid was added, and the reaction was carried out at 90℃ for 48h. The reaction was terminated by cooling to room temperature and exposing to air. Finally, the brush was washed several times by centrifugation with distilled water and dried under vacuum at 80℃ for 10h to obtain the BC-g-NFMPA polymer brush. The preparation method of (N-(2-fluorophenyl)-N-methylacrylamide) is as follows: In a three-necked flask, N-methyl-o-fluoroaniline, triethylamine, p-hydroxyanisole, and anhydrous dichloromethane were added and stirred to dissolve. The mixture was then cooled to 0°C under nitrogen protection. A mixed solution of acryloyl chloride and anhydrous dichloromethane was added dropwise, with a volume ratio of acryloyl chloride to anhydrous dichloromethane of 1:1. The molar ratio of N-methyl-o-fluoroaniline, acryloyl chloride, and triethylamine was 1:1.1:1.3. The amount of p-hydroxyanisole was 0.1 wt% of the acryloyl chloride. After the addition was complete, the mixture was kept at 0°C and stirred for 4 h. Subsequently, the reaction solution was poured into ice water and stirred for 10 min. The mixture was then separated. The organic phase was washed successively with 1 mol / L dilute hydrochloric acid, saturated NaHCO3, and saturated NaCl, dried over anhydrous Na2SO4, filtered, and recrystallized to obtain N-(2-fluorophenyl)-N-methylacrylamide. The NMR spectrum of N-(2-fluorophenyl)-N-methylacrylamide is as follows: Figure 4 As shown in the ¹H NMR spectrum, characteristic hydrogen absorption peaks corresponding to N-methyl, methylene, and fluorophenyl are observed, and each characteristic peak can be matched one-to-one with the molecular structure of N-(2-fluorophenyl)-N-methylacrylamide, proving that the target monomer was successfully synthesized.

[0069] S3. Polymer brush protective layer modified lithium metal anode: 0.5g BC-g-NFMPA was added to 9.5g N,N-dimethylformamide and stirred for 6h to obtain a coating solution. The prepared coating solution was coated on the surface of lithium foil and dried at 60℃ for 10h to obtain a lithium metal battery anode with a polymer brush protective layer.

[0070] Example 3 This embodiment provides a method for preparing a lithium metal anode with a multifunctional polymer brush protective layer, including the following steps: S1. Preparation of BC-Br: Under a nitrogen atmosphere, 6g of BC was mixed with 90g of DMF and 40g of anhydrous triethylamine and stirred for 3h. Then, 30g of BiBB was slowly added dropwise under ice bath conditions and stirred at room temperature for 24h. After washing the product with an ethanol aqueous solution, it was dried under vacuum at 50℃ for 12h to obtain BC-Br.

[0071] S2. Preparation of polymer brush: Under a nitrogen atmosphere, 6g of N-(2-fluorophenyl)-3-methylacrylamide (NF-3MPA), 0.54g of BC-Br, 0.01g of CuBr2, 0.002g of EBiB, 0.26g of pentamethyldiethyltriamine, and 13.108mL of tetrahydrofuran were mixed and stirred at room temperature for 2h. Then, 0.08g of ascorbic acid was added, and the reaction was carried out at 60℃ for 48h. The reaction was terminated by cooling to room temperature and exposing the mixture to air. Finally, the mixture was washed several times by centrifugation with distilled water and dried under vacuum at 60℃ for 5h to obtain the BC-g-NF-3MPA polymer brush. The preparation method of N-(2-fluorophenyl)-3-methylacrylamide is as follows: In a three-necked flask, N-methyl-o-fluoroaniline, triethylamine, p-hydroxyanisole, and anhydrous dichloromethane were added and stirred to dissolve. The mixture was then cooled to 0°C under nitrogen protection. A mixed solution of methacryloyl chloride and anhydrous dichloromethane was added dropwise, with a volume ratio of methacryloyl chloride to anhydrous dichloromethane of 1:1. The molar ratio of N-methyl-o-fluoroaniline, methacryloyl chloride, and triethylamine was 1:1.1:1.4. The amount of p-hydroxyanisole was 0.1 wt% of the methacryloyl chloride. After the addition was complete, the mixture was kept at 20°C and stirred for 4 hours. Subsequently, the reaction solution was poured into ice water and stirred for 10 minutes. The mixture was then separated. The organic phase was washed successively with 1 mol / L dilute hydrochloric acid, saturated NaHCO3, and saturated NaCl, dried over anhydrous Na2SO4, filtered, and recrystallized to obtain N-(2-fluorophenyl)-3-methylacrylamide. The NMR spectrum of N-(2-fluorophenyl)-3-methylacrylamide is as follows: Figure 5 As shown, each characteristic signal in the ¹H NMR spectrum corresponds one-to-one with the molecular structure of N-(2-fluorophenyl)-3-methylacrylamide, indicating that the target monomer was successfully synthesized.

[0072] S3. Polymer brush protective layer modified lithium metal anode: 0.05g BC-g-NF-3MPA was added to 9.95g dimethyl sulfoxide and stirred for 3h to obtain a coating solution. The prepared coating solution was coated on the surface of lithium foil and dried at 80℃ for 6h to obtain a lithium metal battery anode with a polymer brush protective layer.

[0073] Example 4 This embodiment provides a method for preparing a lithium metal anode with a multifunctional polymer brush protective layer, including the following steps: S1. Preparation of BC-Br: Under a nitrogen atmosphere, 6g of BC was mixed with 90g of DMF and 40g of anhydrous triethylamine and stirred for 3h. Then, 30g of BiBB was slowly added dropwise under ice bath conditions and stirred at room temperature for 24h. After washing the product with an ethanol aqueous solution, it was dried under vacuum at 50℃ for 12h to obtain BC-Br.

[0074] S2. Preparation of polymer brush: Under a nitrogen atmosphere, 6g of N-(2-fluorophenyl)-2-hydroxyacrylamide (NFHOPA), 0.5g of BC-Br, 0.01g of CuBr2, 0.004g of EBiB, 0.24g of pentamethyldiethyltriamine, and 13.186mL of methanol were mixed and stirred at room temperature for 1h. Then, 0.06g of ascorbic acid was added, and the reaction was carried out at 90℃ for 36h. The reaction was terminated by cooling to room temperature and exposing the mixture to air. Finally, the mixture was washed several times by centrifugation with distilled water and dried under vacuum at 80℃ for 5h to obtain the BC-g-NFHOPA polymer brush. The preparation method of N-(2-fluorophenyl)-2-hydroxyacrylamide is as follows: N-(2-fluorophenyl)acrylamide was added to formic acid, stirred and dissolved, cooled to 0°C, and 30% hydrogen peroxide was slowly added dropwise. The molar ratio of N-(2-fluorophenyl)acrylamide, hydrogen peroxide and formic acid was 1:1.2:400. The temperature was controlled not to exceed 10°C. The mixture was then stirred at room temperature for 6 hours. The reaction solution was slowly poured into ice water and neutralized to a weakly alkaline state (pH=8) with saturated NaHCO3 while stirring. The organic phase was extracted with ethyl acetate and washed with saturated brine. The solution was dried over anhydrous Na2SO4 and recrystallized to obtain N-(2-fluorophenyl)-2-hydroxyacrylamide. The NMR spectrum of N-(2-fluorophenyl)-2-hydroxyacrylamide is as follows: Figure 6 As shown, the 1H NMR spectrum shows characteristic hydrogen absorption peaks for methylene, hydroxyl, NH and fluorophenyl at the corresponding chemical shifts. All characteristic peaks match the molecular structure of N-(2-fluorophenyl)-2-hydroxyacrylamide, confirming the successful preparation of the target compound.

[0075] S3. Polymer brush protective layer modified lithium metal anode: 0.1g BC-g-NFHOPA was added to 9.9g ethylene glycol dimethyl ether and stirred for 6h to obtain a coating solution. The prepared coating solution was coated on the surface of lithium foil and dried at 60℃ for 10h to obtain a lithium metal battery anode with a polymer brush protective layer.

[0076] Example 5 This embodiment provides a method for preparing a lithium metal anode with a multifunctional polymer brush protective layer, including the following steps: S1. Preparation of BC-Br: Under a nitrogen atmosphere, 6g of BC was mixed with 90g of DMF and 40g of anhydrous triethylamine and stirred for 3h. Then, 30g of BiBB was slowly added dropwise under ice bath conditions and stirred at room temperature for 24h. After washing the product with an ethanol aqueous solution, it was dried under vacuum at 50℃ for 12h to obtain BC-Br.

[0077] S2. Preparation of polymer brush: Under a nitrogen atmosphere, 7g of N-(2-fluorophenyl)-N-ethyl-N-methylacrylamide (NFEMPA), 0.6g of BC-Br, 0.012g of CuBr2, 0.006g of BMBz, 0.32g of bpy and 12mL of N,N-dimethylformamide were mixed and stirred at room temperature for 3h. Then, 0.062g of ascorbic acid was added, and the reaction was carried out at 70℃ for 36h. The reaction was terminated by cooling to room temperature and exposing to air. Finally, the brush was washed several times by centrifugation with distilled water and dried under vacuum at 70℃ for 8.5h to obtain the BC-g-NFEMPA polymer brush. The preparation method of N-(2-fluorophenyl)-N-ethyl-N-methylacrylamide is as follows: In a three-necked flask, N-ethyl-2-fluoroaniline, triethylamine, p-hydroxyanisole, and anhydrous dichloromethane were added and stirred to dissolve. The mixture was then cooled to 0°C under nitrogen protection. Acryloyl chloride was slowly added dropwise. The volume ratio of N-ethyl-2-fluoroaniline to anhydrous dichloromethane was 1:10, and the molar ratio of N-ethyl-2-fluoroaniline, acryloyl chloride, and triethylamine was 1:1.1:1.5. The amount of p-hydroxyanisole was 0.1 wt% of the acryloyl chloride. After the addition was complete, the mixture was kept at 20°C and stirred for 4 hours. Subsequently, the reaction solution was poured into ice water and stirred for 10 minutes. The mixture was then separated. The organic phase was washed successively with 1 mol / L dilute hydrochloric acid, saturated NaHCO3, and saturated NaCl. After drying with anhydrous Na2SO4 and filtration, N-(2-fluorophenyl)-N-ethyl-N-methylacrylamide was obtained. The NMR spectrum of N-(2-fluorophenyl)-N-ethyl-N-methylacrylamide is as follows: Figure 7 As shown in the ¹H NMR spectrum, characteristic hydrogen absorption peaks corresponding to N-ethyl, N-methyl, methylene and fluorophenyl appear sequentially at different chemical shifts. Each characteristic peak corresponds one-to-one with the molecular structure of N-(2-fluorophenyl)-N-ethyl-N-methylacrylamide, which proves that the target monomer was successfully synthesized.

[0078] S3. Polymer brush protective layer modified lithium metal anode: 0.3g BC-g-NFEMPA was added to 9.7g 1,3-dioxolane and stirred for 6h to obtain a coating solution. The prepared coating solution was coated on the surface of lithium foil and dried at 75℃ for 7h to obtain a lithium metal battery anode with a polymer brush protective layer.

[0079] Comparative Example Comparative Example 1 The only difference between this comparative example and Example 1 is that the polymer brush protective layer is omitted, and lithium foil is used directly as the negative electrode of the lithium metal battery.

[0080] Comparative Example 2 This comparative example provides a method for preparing a lithium metal anode with a protective layer, comprising the following steps: S1. 100 mg of graphene oxide (rGO) and 2 mL of triethylamine were dispersed in 100 mL of anhydrous DMF, sonicated in an ice bath for 30 min, 1.2 mL of 2-bromoisobutyryl bromide was added dropwise, stirred at 0 °C for 2 h, and reacted at room temperature for 24 h. After centrifugation at 2000 r / min, the mixture was washed three times each with DMF, ethanol, and deionized water, and then freeze-dried to obtain GO-Br. S2. Disperse 50 mg of GO-Br obtained in step S1 in 50 mL of anhydrous DMF, add 0.05 g of pentamethyldiethylenetriamine, 1 g of methacrylic acid (MA), and 0.4 g of 2,2,2-trifluoroethyl acrylate (TFEA), degas three times, then add 0.03 g of cuprous bromide and 0.02 g of ascorbic acid, react at 60 °C under argon protection for 24 h, filter through a 0.22 μm filter membrane, wash successively with DMF, methanol, and deionized water until the filtrate is colorless, and lyophilize to obtain GO-gP (TFEA-co-MA); 20 mg GO-gP(TFEA-co-MA) was dispersed in 2 mL of anhydrous dimethyl sulfoxide to prepare a solution (0.01 g / mL). 100 μL of the solvent was dropped onto the surface of the lithium foil and spin-coated at 2000 rpm for 30 s. Then, 100 μL of the solution was spin-coated for 60 s and treated at 100 °C for 30 min to obtain a lithium metal anode with an artificial SEI film.

[0081] Comparative Example 3 The only difference between this comparative example and Example 1 is that an equal amount of p-fluorostyrene was used to replace N-(2-fluorophenyl)acrylamide. The specific steps are as follows: S1. Preparation of BC-Br: Under a nitrogen atmosphere, 6g of BC was mixed with 90g of DMF and 40g of anhydrous triethylamine and stirred for 3h. Then, 30g of BiBB was slowly added dropwise under ice bath conditions and stirred at room temperature for 24h. After washing the product with an ethanol aqueous solution, it was dried under vacuum at 50℃ for 12h to obtain BC-Br. S2. Preparation of polymer brush: Under a nitrogen atmosphere, 5g of p-fluorostyrene, 0.6g of BC-Br, 0.012g of CuBr2, 0.004g of BMBz, 0.314g of pentamethyldiethyltriamine and 14mL of N,N-dimethylformamide were mixed and stirred at room temperature for 3h. Then, 0.07g of ascorbic acid was added, and the mixture was reacted at 80℃ for 24h. After cooling to room temperature, the reaction was terminated by exposure to air. Finally, the mixture was washed several times by centrifugation with distilled water and dried under vacuum at 70℃ for 8h to obtain the BC-g-p-fluorostyrene polymer brush. S3. Polymer brush protective layer modified lithium metal anode: 0.3g BC-g-p-fluorostyrene was added to 9.7g tetrahydrofuran and stirred for 4h to obtain a coating solution. The prepared coating solution was coated on the surface of lithium foil and dried at 80℃ for 6h to obtain a lithium metal battery anode with a polymer brush protective layer.

[0082] Comparative Example 4 The only difference between this comparative example and Example 1 is that an equal amount of methacrylamide was used to replace N-(2-fluorophenyl)acrylamide. The specific steps are as follows: S1. Preparation of BC-Br: Under a nitrogen atmosphere, 6g of BC was mixed with 90g of DMF and 40g of anhydrous triethylamine and stirred for 3h. Then, 30g of BiBB was slowly added dropwise under ice bath conditions and stirred at room temperature for 24h. After washing the product with an ethanol aqueous solution, it was dried under vacuum at 50℃ for 12h to obtain BC-Br. S2. Preparation of polymer brush: Under a nitrogen atmosphere, 5g of methacrylamide, 0.6g of BC-Br, 0.012g of CuBr2, 0.004g of BMBz, 0.314g of pentamethyldiethyltriamine and 14mL of N,N-dimethylformamide were mixed and stirred at room temperature for 3h. Then, 0.07g of ascorbic acid was added, and the mixture was reacted at 80℃ for 24h. After cooling to room temperature, the reaction was terminated by exposure to air. Finally, the mixture was washed several times by centrifugation with distilled water and dried under vacuum at 70℃ for 8h to obtain the BC-g-methacrylamide polymer brush. S3. Polymer brush protective layer modified lithium metal anode: 0.3g BC-g-methacrylamide was added to 9.7g tetrahydrofuran and stirred for 4h to obtain a coating solution. The prepared coating solution was coated on the surface of lithium foil and dried at 80℃ for 6h to obtain a lithium metal battery anode with a polymer brush protective layer.

[0083] Comparative Example 5 The only difference between this comparative example and Example 1 is that BC is used directly as the protective layer. The specific steps are as follows: 0.3g of BC was added to 9.7g of tetrahydrofuran and stirred for 4 hours to obtain a coating solution. The prepared coating solution was coated on the surface of lithium foil and dried at 80°C for 6 hours to obtain a lithium metal battery negative electrode with a BC protective layer.

[0084] Test case The lithium metal battery anodes prepared in Examples 1-5 and Comparative Examples 1-5 were assembled with Celgard 2400 separators, NCM811 cathodes, and conventional carbonate electrolytes (1M LiPF6, EC / DMC / FEC (v / v / v = 3 / 7 / 0.5)) into 3.5Ah pouch cells, and their electrochemical performance was tested. The test conditions were 3-4.3V, 0.2C / 0.5C charge-discharge cycles 200 times. The test data are shown in Table 1.

[0085] Table 1. Measurement results of battery voltage, internal resistance, and cycle performance in the examples and comparative examples.

[0086] As can be seen from Table 1, the overall performance of the batteries prepared in Examples 1-5 is better than that of Comparative Examples 1-5.

[0087] Comparing the test results of Examples 1-5 with Comparative Example 1, it can be seen that the battery composed of a lithium metal anode with a polymer brush protective layer can significantly improve the polarization voltage and cycle stability of the lithium metal battery. This is mainly because the polymer brush protective layer provided by the present invention has high conductivity and excellent mechanical properties, induces the formation of a rigid high lithium-ion conductivity inner layer rich in LiF and LiN, inhibits the formation of lithium dendrites, and ultimately achieves effective protection of the lithium metal anode and improves the cycle performance of the lithium metal battery.

[0088] In Comparative Example 2, a lithium metal anode with an artificial SEI was prepared using the method described in patent CN120809731A. The polarization voltage and internal resistance of Comparative Example 2 were significantly higher than those of the Example, while the capacity retention was slightly lower. This is because the densely packed two-dimensional stacked graphene oxide sheets in Comparative Example 2 could not effectively alleviate the volume expansion of the anode, and there were no nitrogen-containing functional groups, resulting in fewer derived lithium nitrides. Although this could improve cycle performance based on a pure lithium anode, the lithium-ion conductivity at the inorganic interface was low, and lithium-ion transport in the fluorinated inorganic layer was slow and uneven, leading to insignificant optimization of the battery's internal resistance.

[0089] Comparative Example 3 uses a polymer brush containing only fluorinated phenyl groups to modify the lithium metal anode, thus the derived inorganic layer contains abundant lithium fluoride. However, the battery internal resistance and polarization are relatively high. This is because the lithium ion conductivity of lithium fluoride is poor, so the battery cycle performance is not as good as that of the Example.

[0090] Comparative Example 4 uses a nitrogen-containing polymer brush that does not contain fluorinated phenyl groups, thus the derived inorganic interface has a high ionic conductivity, but its stability is limited, resulting in no significant improvement in battery cycle performance.

[0091] The lithium metal anode modification layer in Comparative Example 5 uses BC, which does not contain polymer brushes. This only alleviates anode volume expansion but cannot effectively regulate ion transport, thus having limited effect on improving battery cycle stability. Therefore, using bacterial cellulose to alleviate anode volume expansion and grafting fluorine-nitrogen-containing polymer brushes to derive a lithium fluoride / lithium nitride hybrid layer are necessary to reduce battery internal resistance and improve cycle performance.

[0092] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for preparing a lithium metal anode containing a multifunctional polymer brush protective layer, characterized in that, Includes the following steps: S1. Preparation of BC-Br; S2. Preparation of polymer brush: Under an inert atmosphere, BC-Br is mixed and stirred with N-(2-fluorophenyl)acrylamide monomers, catalyst, initiator, ligand, and solvent. Then ascorbic acid is added to obtain a mixture. The mixture is reacted, cooled, washed, and dried to obtain a polymer brush. In step S2, the N-(2-fluorophenyl)acrylamide monomers include any one or more of N-(2-fluorophenyl)acrylamide, N-(2-fluorophenyl)-N-methylacrylamide, N-(2-fluorophenyl)-3-methylacrylamide, N-(2-fluorophenyl)-2-hydroxyacrylamide, and N-(2-fluorophenyl)-N-ethyl-N-methylacrylamide; S3. Modification of lithium metal anode with polymer brush protective layer: Disperse the polymer brush obtained in step S2 in an organic solvent, stir to obtain a coating solution, apply the coating solution to the surface of lithium metal, and dry to obtain a lithium metal battery anode with polymer brush protective layer.

2. The method for preparing a lithium metal anode with a multifunctional polymer brush protective layer as described in claim 1, characterized in that, In step S1, the preparation method of BC-Br is as follows: Under a nitrogen atmosphere, BC, DMF and anhydrous triethylamine were mixed and stirred. Then, BiBB was added dropwise, stirred at room temperature, washed and dried to obtain BC-Br.

3. The method for preparing a lithium metal anode with a multifunctional polymer brush protective layer as described in claim 2, characterized in that, The ratio of BC, DMF, anhydrous triethylamine, and BiBB is 6g:90mL:40g:30g; The mixing and stirring time is 2 to 4 hours; The stirring time at room temperature is 20–28 hours.

4. The method for preparing a lithium metal anode with a multifunctional polymer brush protective layer as described in claim 1, characterized in that, In step S2, the catalyst includes any one or more of CuBr2 and CuBr; The initiator includes any one or more of bromomethylbenzoate, ethyl bromophenylacetate, and ethyl bromoisobutyrate. The ligand includes any one or more of 2,2'-bipyridine and pentamethyldiethyltriamine; The solvent includes any one or more of N,N-dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, and methanol; The inert atmosphere is nitrogen.

5. The method for preparing a lithium metal anode with a multifunctional polymer brush protective layer as described in claim 1, characterized in that, In step S2, based on the total mass of the mixture, the mass percentages of each component are as follows: N-(2-fluorophenyl)acrylamide monomers 25%–35%, BC-Br 2.5%–3%, catalyst 0.05%–0.06%, initiator 0.01%–0.03%, ligand 1.2%–1.6%, organic solvent 60%–70%, and ascorbic acid 0.3%–0.4%.

6. The method for preparing a lithium metal anode with a multifunctional polymer brush protective layer as described in claim 1, characterized in that, In step S2, the mixing and stirring time is 1 to 3 hours; The reaction time is 24–48 h, and the temperature is 60–90 °C; The drying temperature is 60–80°C, and the time is 5–10 hours.

7. The method for preparing a lithium metal anode with a multifunctional polymer brush protective layer as described in claim 1, characterized in that, In step S3, the organic solvent includes any one or more of tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide, ethylene glycol dimethyl ether, and 1,3-dioxolane. The polymer brush has a mass percentage of 0.5% to 5% in the coating solution; The stirring time is 3 to 6 hours; The drying temperature is 60–80°C, and the time is 6–10 hours.

8. A lithium metal anode containing a multifunctional polymer brush protective layer, characterized in that, It is prepared by the preparation method according to any one of claims 1-7.

9. A lithium metal battery, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode is the lithium metal negative electrode with a multifunctional polymer brush protective layer as described in claim 8.

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